I will try with an idling controller on split-screen again first, but the glitch only seems to work most of the time and once the arms are removed it seems to stop working. It may be dependent on where he ends up after moving to the decoy I send up in the lift if he can detect my presence.

I should maybe get some other weapons for the guest brick I'm using, so he can deal some extra damage but he's so low level it'd barely be worth it on a level 65+ boss.

I went with brick to use the berserker rage health bonus/damage reduction bit so he would survive and be a distraction for longer, but you seem to need to hit crawmerax to make him lumber for you. The siren might be much better indeed.